A new study backs up a suggestion that high dosages of aspirin may interfere with AstraZeneca's heart drug Brilinta, offering a possible explanation for disappointing results from a trial among patients in North America. The potential multibillion dollar drug is already approved in 33 countries, but the prospects of a green light from U.S, regulators have been clouded by a trial that appeared to show it performed worse than rival drug Plavix. Experts have speculated that the lack of effect in U.S. patients might be due to the drug's interaction with aspirin, which is typically given in higher doses alongside treatments such as Plavix in the United States than in Europe.